1. Field of the Invention
The invention relates to a pixel structure and a fabrication method thereof, and more particularly relates to a pixel structure having an oxide semiconductor layer and a fabrication method thereof.
2. Description of Related Art
The common flat displays include the liquid crystal displays (LCD), the plasma displays, the organic light emitting diode displays, and so on. Regarding to the popular LCD, the LCD is mainly composed of a thin film transistor (TFT) array substrate, a color filter substrate, and a liquid crystal layer sandwiched between said two substrates. On the TFT array substrate, the amorphous silicon (a-Si) TFT or the low temperature poly-silicon (LTPS) TFT are selected to serve as the switching element in each sub-pixel. Recently, the researches direct that the oxide semiconductor TFT has higher carrier mobility relative to the a-Si TFT and has better threshold voltage (Vth) consistency relative to the LTPS TFT. Therefore, the oxide semiconductor TFT is supposed to become the main switching element of the flat displays in the coming generation.
In the oxide semiconductor TFT, the source and the drain in contact with the oxide semiconductor are usually made of metal material. As for the known fabrication method, the etchant for patterning the metal material has low etching selectivity ratio of the oxide semiconductor to the metal material. Accordingly, the oxide semiconductor usually is etched by the etchant during patterning the metal material when the source and the drain are fabricated above the oxide semiconductor, which causes poor channel property of the oxide semiconductor. Furthermore, the oxygen utilizing for forming the oxide semiconductor would oxidize the surface of the source and the drain when the oxide semiconductor is fabricated above the source and the drain, and thus the contact resistance of the source and the drain in contact with the oxide semiconductor is increased, which has negative influence on the element characteristics of the TFTs.